This invention relates generally to digital display apparatus, and particularly relates to such apparatus having means for minimizing the jitter which may otherwise occur in the last digit.
A digital speedometer has certain obvious advantages over a conventional instrument with a pointer because it presents data to the observer in a form which is easily read and which is unambigious. Thus instead of having to estimate the precise speed it can now be read in exact numbers. This applies to any digital display whether it is a speedometer, a frequency counter, an event counter or the like. In other words, it applies to any apparatus which digitally displays pulses having a variable repetition rate.
The digital speedometer may, for example, form part of a digital speed control system. Such speed control systems have become well known in the art, an example being the patent to Carol, Jr. et al., U.S. Pat. No. 3,599,154.
The jitter in a digital speedometer may be caused by the fact that the speed pulses representative of the speed of the vehicle are by necessity not synchronized with the clock pulses which control the operation of the system. Even if the speed pulses were synchronized with the clock pulses, this would only apply to one particular speed. The result is that even if the speed is constant the last digit is subject to jitter, that is the last number may vary at random between say three and four or two and three.
The jitter may also be caused by a backlash in the gear drive train which acts as the speed pulse generator. This may cause variations in the pulse rate even if the speed is constant.
Even if the actual speed of the vehicle is not actually constant, minimizing of jitter or rapid change of the last displayed digit would be useful. This is particularly true when an automobile, for example, accelerates or decelerates.
It is accordingly an object of the present invention to provide an improved digital display apparatus having means for minimizing the jitter of the last displayed digit which may otherwise occur.